Zhu, Z. (Corresponding author)

1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Report No.: JUEL-3109

Abstract: Ceramic materials including Al$_{2}$O$_{3}$, SiC, AIN, Si$_{3}$N$_{4}$, MgO, MgAl$_{2}$O$_{4}$, Si and SiO$_{2}$ as wen as the refractory metal tungsten are irradiated with protons in the 10 MeV energy range at temperatures from 75°C to 630°C under uniaxial tensile stresses from 6 to 330 MPa to dose levels up to about 0.1 dpa. Changes in length and electrical resistivity are monitored after each irradiation or during beam-off periods. TEM and optical absorption technique are applied to extract information on the radiation induced microstructural changes. For materials with crystalline structure a modified rate theory is used to discuss the measurements whereas for SiO$_{2}$ glass a model is developed to describe the radiation induced deformation(compaction) and viscous flow. Alternatively a recently developed visco-elastic model based on thermal spike formation is also applied to explain the observed viscous flow in SiO$_{2}$ glass. It is found that crystalline materials irradiated in the intermediate temperature range (0.2T$_{m}$ < T$_{irr}$ < 0.4T$_{m}$) deform in four different stages: (1) At very low doses mainly point defects or small defect clusters (loops) are formed, the strain increases linearly with dose. (2) After the nucleation of interstitial-type loops has finished and they become the dominating sinks, the strain follows a 2/3 power law dose dependence. (3) The growth and intersection of loops resulting in the formation of dislocation networks leads to a 1/2 dose dependence of the strain. (4) Finally, the strain saturates when the vacancy concentration becomes so high that spontaneous recombination dominates. Thermal spike formation can account for at most 10% of the observed viscous flow of vitreous SiO$_{2}$ under 9.2 MeV proton irradiation. It is therefore proposed that energy deposition through electronic processes must also contribute to the viscous flow in glassy materials through processes of bond-breaking and re-bonding during irradiation. Formation of new bonds results in deformation while re arrangements of atoms with respect to the direction of an external stress during re-bonding causes viscous flow. Furthermore, the present study demonstrates indirectly that the so-called RIED effect(radiation induced dectrical degradation) in Al$_{2}$O$_{3}$ could be due to surface contamination which is enhanced by the applied electrical field.

1. Institut für Festkörperforschung (IFF)